'Cartouche' is actually a French word meaning 'gun cartridge'. When Napoleon's soldiers were in Egypt, they nicknamed this shape 'cartouche' because it reminded them of the shape of their gun cartridges, or bullets. At the time, people could not read hieroglyphic writing, so they did not know that the cartouche surrounded the name of the pharaoh. 'Cartouche' became so commonly used that it has remained the standard name for the shape around the name of an Egyptian pharaoh or queen.

Were royal names always written inside cartouches?

In the first three dynasties, royal names were written inside a rectangle called a 'serekh'. The bottom half of the rectangle was filled with a picture of the front of the royal palace. The top half was filled with the hieroglyphs for the king's name. On the top of the box sat the god Horus, who was identified with the pharaoh throughout Egyptian history.